A typical yoga class is a group of people working with a yoga teacher usually for one and a half hours. People wear comfortable clothing that allows for complete freedom of movement.
Yoga is best practiced with bare feet. Often a class begins with movement that "invites" the body to warm through gentle moving. From there you could expect a balanced program of postures or asanas that can be defined as a "physical positioning that co-ordinates breathing with moving and holding still for the purpose of both stretching and strengthening parts of the body" (Judith Lassiter, contributing, "Living Yoga").
The basic movements of yoga include extension, flexion, rotation, and lateral flexion. They are done standing, seated and sometimes inverted.
After the active part of the class, most yoga classes conclude with a period of relaxation and sometimes meditation.
The atmosphere in a yoga class should be non-competative with an emphasis on adapting postures to the person and not the person to the posture. Well trained teachers feel free to use chairs, blankets, belts, and even cushions to help with any problems. Individual assistance should be freely offered. However a person with strong needs should perhaps consider a private consultaion.